2010-11-16

Spirit Sol 665

Ah, heck. We meant to make 60m of progress, and came up with only 37m.

How did this happen? Let's see, autonav imaging takes roughly 3 minutes per 50cm step, which means we should expect to take 20 such steps per hour, or -- oops -- 10m per hour. And we spent two hours on autonav, as predicted, and thus made only about 20m of progress in that time.

Both Ashitey and I were remembering that autonav makes more like 35m per hour. But this is true only when we turn on a feature called "step-skipping." Instead of "image, step, image, step," it does "image, step, step, image, step, step," or even "image, step, step, step, image, step, step, step." Since the "image" part is the slow part, this makes a dramatic improvement in how fast we can drive.

But since this is less safe, since the rover moves farther before taking images of the world around it, it's not the default.

Duh.

Thisol we decide we'll turn on step-skipping.

To make matters worse, we had a poor downlink, and we have more data products on board than we'd like. (We have to worry not only about the total amount of data on the rover but also the number of separate data products.) SOWG chair John Grant proposes cutting the drive short as a way of reducing the generation of new data products until some old ones can be downlinked.

"Nah," I say, "we're not gonna do that."

"But if we don't, the rover will start autodeleting old science products," Emily Eelkema chimes in.

That's what I was waiting for. Since it's been on my mind, I say: "Forget those old MI images! They're history! Let it go! Embrace change!"

They cut the drive short.

Well, it won't be too bad. With step-skipping on, we'll make the same amount of distance as today (about 40m) in the shortened time -- still a decent amount to show for ourselves.

As long as we're changing things in the sequence ... a significant contributor to the drive time is the periodic slip-check sequence. Since it has to invoke visodom, and all the complex 3-D processing that goes along with it, this tends to chew up a lot of duration. What's more, since we're now fairly confident we can make it all the way downhill, most of the original rationale for the slip checks (ensuring we'd be able to make it back to the top of Husband Hill if we got into a bad spot along the way) has disappeared. So I ask Ashitey what he thinks about taking them out.

"Maybe after the Martian-year anniversary," he says. It's next week. "We want both rovers healthy for that."

This is wisdom. I let it go.

Late in the day, Justin Maki points out an article on the Aviation Week Web site. It's something Craig Covault wrote about his recent visit. I didn't realize it at the time, but he was still here for our big discussion about IDDing Hillary.

Emily seems a little worried about the article, but I'm not. "I'm glad he was here for that," I say. "I think it shows us at our best. We had a real concern about a genuinely difficult and novel problem, we took it seriously, we did the analysis we had to do, we proceeded with the right degree of caution -- and in the end, we got the science."

Covault's article is hampered somewhat by the fact that he was on the other end of a teleconference, listening to unfamiliar voices. As a result, some of the details get smudged. But taking that into account, I think he got the big things right: our dedication, our talent, our -- well, damn it, I'm not ashamed to say our brilliance.

Because we're damn good at this. Even if we do forget to turn on step-skipping once in a while.